You would find if Germany tried to exit they would be taken to the European High Court. Ultimately they are a sovereign nation and can do what ever they want but they would want to have the military ready to backup any form of exodus of Europe as it will get ugly.
this is true. I guess if the rumours of mark printing are true they will take the risk, it would obliteration the euro before anything could be decided in the euro court. The announcement will be backed up by immediate bank holiday in europe to stop a run on the french, italian etc banks. The euro will be dead instantly and there won't be anything to fight over.
The other thing is that it is not the germans fault the greek, spanish governments were reckless and so it would be politically possible to push it through.